(A) Field of the Invention
The present invention relates to a light emitting diode (LED) apparatus, and more particularly to an LED apparatus with temperature control and current regulation functions.
(B) Description of the Related Art
In recent years, white LEDs have become a very popular new product attracting widespread attention all over the world. Because white LEDs offer the advantages of small size, low power consumption, long life, and quick response speed, the problems of conventional incandescent bulbs can be solved. Therefore, the applications of LEDs in backlight sources of displays, mini-projectors, illumination, and car lamp sources are becoming increasingly important in the market.
Although LEDs represent the future of illumination applications, many problems still remain unsolved. For example, with a high power LED for illumination, only about 15-20% of input power is converted into light, and the remaining 80-85% is converted into heat. If the heat is not dissipated to the environment efficiently, the temperature of the LED die will be too high, thus influencing the light emitting intensity and service life of the LED die.
FIG. 1 shows the current, voltage, and temperature conditions of a single LED die when an operation voltage of 4V and current of 1.8 A are applied. After applying such voltage and current, the temperature of the LED die rises from 30° C. to 80° C. in 10 minutes, and will continue to rise, eventually causing the LED to over-heat.
Conventionally, in order to solve the problem of overheating of the LED die, a resistor is serially connected. However, being less sensitive to temperature change, the resistor has neither temperature-sensing nor current-regulation functions, so that the effect is not satisfactory, and cannot provide a stable current within a safe range to protect the LED die.
Moreover, the light emission patterns of red (R), green (G), and blue (B) LED dies are different at high and low temperatures, so the difference in temperature will lead to unexpected R, G, and B color differences, causing color distortion due to imprecise mixing of the three colors. Conventionally, current limiting for the LED die is performed with a power IC to prevent battery overheating, and the color difference is modified depending on a color compensation circuit and a control IC. However, the power IC, the color compensation circuit, and the control IC techniques are complicated and expensive; thus creating a limitation to the popularity of the application of LEDs.
In view of the above, it is crucial for the popularity of LEDs to solve the problems of heat generation and color difference of the emitted light in LED applications.